This invention relates to a process for guiding quench air into a quench chamber to cool and solidify filaments and filament bundles. It also relates to quench chambers in which quench air is mainly blown perpendicular to the average thread path axis. Air quenching of melt spun filaments by passing air across the filament bundle is well-known. It is also known that this air stream should be laminar, and that the air velocity profile in vertical direction (thread path direction) can vary according to the particular process. However, the horizontal air velocity profile should be constant. The quench chamber normally has two side walls which serve both to prevent the cross-flowing air from escaping into the factory room and to avoid disturbance of the uniform conditions inside the quench cabinet caused by drafts in surrounding room. For this purpose, the front wall of the cooling duct is made air permeable. The threads or thread bundles are drawn into a floor interconnection tube where they are again protected against outside air influences. This protection is necessary to avoid thread oscillations which can influence the sensitive upper portion of the filaments much as occurs with waves on an oscillating string.
Normally, the filament bundle in the quench chamber forms a certain air resistance system, in which a large part of the air follows the path of least resistance and passes outside of the filament bundle. This bypassing air is not available for air quenching itself, since it does not pass by the bundle closely enough to have a cooling effect. In addition, the boundary zone near the wall channels and accelerates the evading flow creating a speed gradient running perpendicular to the flow direction which causes a transition into turbulence and leads to strong fluttering of the outer filaments of the bundle.
For the usual practice of supplying the quench chamber from an air supply entrance through an air supply box and rectifier to the vicinity of the filament bundle, the air flow boundary layer thickness increases along the wall by the square root of the running length of the air, usually reaching values of between 20 and 40 mm. (See L. Prandtl, "Fluid Dynamics", 4th edition 1944, page 99, FIG. 91).
The objective of this invention to influence the course of cooling of the filaments or filament bundle in the quench duct in such a way that the filaments are cooled equally over the entire width and height of the quench duct. It is a further object that the cross-running cooling air is not forced to significantly deviate from its flow path through the filaments. According to this invention, a relatively small free-flow space is formed for the cooling air stream between the outer side of the filament bundle and the quench duct limiting walls. The width of this free-flow space corresponds to the distance between the single filaments of a filament row and is usually between 10 to 15 mm, with a maximum of 25 mm. For this purpose, intermediate limiting walls or wings at the sides of the quench chamber are set at the aforementioned distance from the outer filaments of the filament bundle.
By setting the side limiting walls of the quench duct closer to the outer filaments of the filament bundle, the cooling air can no longer freely pass between the outer filaments and the walls. Instead, it is forced to find its way between the single filaments of the bundle itself. Therefore, the flow of the air becomes more evenly distributed, and the cooling effect is considerably improved. By eliminating the formation of a side stream, there is an essential improvement in the efficiency of the cooling process, since the threads cool more rapidly. Because variations exist in the kind of polymer being spun into filaments and in the melt temperature, it will not always be possible to use the same distance to the sidewalls as between the filament rows. This is because the melt spun filaments can be sticky at points between the spinneret and where the polymer solidifies, causing the process to stop if an oscillating filament should touch the side wall. Thus there are optimum distances between the filaments in the bundle and between the outer filaments and the intermediate limiting side walls. Distances of about 10-25 mm, depending on width of the filament bundle, usually provide adequately safe and uniform flow through the filament bundle.
It should be remembered that the distance between the outer filaments and the limiting walls of the quench duct remains constant along the entire vertical height of the air supply from the rectifier to the filament, thus providing optimum conditions along the entire filament bundle.
An additional improvement of this invention is the inner air guiding wings located inside of the outer quench chamber walls. These wings are kept at a constant distance form the outermost threads of the filament bundle. Preferably the angle followed by the inner air limitation wings is the same as that of the contractable path of the thread bundle. Specifically, the inner wings should be inclined downwardly towards the vertical center line of the quench chamber, thus converging at the bottom. Thus, the chamber's horizontal cross section can be kept retangular. The separate inner air limiting wings allow the optimum conditions of each operation to be adjusted and set so that a uniform air flow always passes through the bundle. This optimization is also possible where several multifilaments with parallel vertical center lines or with slightly downwards convergent center lines are to be cooled and solidified.
Similar conditions can be arranged at the supply side of the air rectifier and quench chamber by arranging air stream wings in the plenum which are in alignment with the air stream limiting wings of the quench chamber.
This invention can also be used in cases where threads are drawn upwards from the spinnerets. In such cases the above-mentioned air limiting wings at the air supply side and in the quench chamber provide the same advantageous conditions for upward drawing as for the corresponding downward drawing systems.